The present invention relates to an in-line data comunication system, wherein terminal stations are connected to each other via a bidirectional communication cable.
In such an in-line data communication system, signal attenuation creates a serious problem when a long communication cable is used to connect long-distanced terminal stations. The signal attenuation is mainly caused by the impedance of the communication cable. To reduce the signal attenuation, one approach of the conventional system is to employ a communication cable of low impedance. Such a communication cable makes the system expensive. Another approach in the conventional system is to employ two communication cables, one for data transmission and the other for data reception. Amplifying circuits are connected to the transmission cable and the reception cable, respectively. This complicates the construction of the data communication system.
Accordingly, an object of the present invention is to provide an in-line data communication system which ensures accurate data communication.
Another object of the present invention is to provide a signal level compensation system disposed in a bidirectional communication cable which connectes terminal stations.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a bidirectional communication cable (coaxial cable) is employed to connect terminal stations with each other. A signal level compensation circuit is disposed between the terminal stations and is connected to the bidirectional communication cable. The signal level compensation circuit includes first and second amplifying circuits. The first amplifying circuit is enabled and the second amlifying circuit is disabled when a data signal is transmitted in one direction within the bidirectional communication cable, thereby compensating for the signal attenuation in one direction. The first amplifying circuit is disabled and the second amplifying circuit is enabled when the data signal is transmitted in the opposing direction within the bidirection cable, thereby compensating for the signal attenuation in the opposing direction. The first and second amplifying circuits are disposed in the signal level compensation circuit in a parallel fashion with each other so that the signal level compensation circuit has a pair of terminals connected to the bidirectional communication cable.